I'm working on a new painting, and was wondering about the combination of different paints...

You can use acrylics on top of or with watercolor paints because they are both water based. Acrylic put on top of watercolor would not hurt the watercolor, and could work nicely for putting in areas of bold or deep color when the watercolors have dried. Depending on the thickness of the acrylic paint (how much water you put into it or not), it could cover the watercolor work completely.... but perhaps you want that effect? I would suggest that you do experiments with how much water to put into acrylic paint if you want to make acrylic color washes over watercolor washes.